American Forests 1996. The 1996-1997 National Register of Big Trees. Washington, DC: American Forests.
The big tree register is now (2009.04.13) available online: click HERE.
I've said this elsewhere on the site, but here's the disclaimer: the American Forests big tree list is highly biased and contains numerous errors. The bias stems from the way that they measure big trees, which is to sum the tree's circumference in inches, its height in feet, and the average crown diameter in feet. Trees with multiple stems are included as long as the stems unite above ground, and if the stems unite below breast height, then diameter is measured as the smallest diameter measurable below breast height. Thus a tree is likely to win the title of "big tree" if it has multiple stem that join just above ground level, and at least some of the stems lean far outwards, producing a large crown diameter. The "big tree" list thus contains a disproportionate number of multiple-stem trees, with trees having much larger single stems commonly being passed over. Second, as I mentioned, the list contains numerous errors. Examples include misidentifications (much more common among hardwoods than conifers), and sometimes wildly overestimated tree heights. This list also uses an antiquated taxonomy that hasn't been revised since at least the 1970s. However, the "big tree" list still is useful because it gives an idea of the approximate maximum sizes that can be attained by these trees. With time, perhaps the biases and the errors can be reduced, and the list can become a more accurate inventory of the largest known American trees.